Various embodiments of the inventive concept comprise molecular sieve blends containing a combination of a zeolite with a halloysite clay binder. Various zeolites can be utilized in the preparation of the molecular sieve blends thereof, and various processes of manufacture and use of these molecular sieve blends exist. Some preferred uses include production of oxygen from ambient air for medical, industrial and commercial purposes, dehydration of liquid and gaseous hydrocarbon streams, drying of cracked C1-C4 hydrocarbon gas streams, dehydration of ethanol, and removal of various undesired materials from various types of hydrocarbon feed streams. (For purpose of this disclosure “molecular sieve blends” may alternatively be referred to as “adsorbents”, “adsorbent blends”, “molecular sieve adsorbent blends” zeolite blends, adsorbent zeolite blends or “molecular sieve adsorbents” or such similar terms.)
Zeolites are hydrated metal alumino silicates having the general formulaM2/nO:Al2O3:xSiO2:yH2Owhere M usually represents a metal, preferably of the alkali or alkaline earth group, n is the valence of the metal M, x varies from 2 to infinity, depending on the zeolite structural type and y designates the hydrated status of the zeolite.
Most zeolites are three-dimensional crystals with a crystal size in the range of 0.1 to 30 μm. Heating these zeolites to high temperatures results in the loss of the water of hydration, leaving a crystalline structure with channels of molecular dimensions, offering a high surface area for the adsorption of inorganic or organic molecules. Adsorption of particular molecules is dependent upon the size of these zeolite channels. The rate of adsorption is limited by the laws of diffusion.
Zeolites are used for a number of processes. The choice of the zeolite is important in a number of processes well known to those skilled in the art. Zeolites with and without binders are used for dehydration, adsorption of various compounds from feed streams and separation of various hydrocarbons from a feed stream. Various kinds of clays have been utilized to produce binderless molecular sieves.
Molecular sieves blends have also been advantageous for a number of processes as the diffusion of materials into and out of the pores can be facilitated based on the pore size that is present within the particular molecular sieve. (For purposes of this disclosure “zeolite” and “molecular sieve” have the same meaning.)
One limitation on the utilization of zeolites is their extremely fine particle size. Large, naturally-formed agglomerates of zeolite crystals break apart easily. In addition, because the pressure drop through a bed containing only such fine zeolite crystals is prohibitively high, these zeolite crystals are not used alone in fixed beds for various dynamic applications, such as production of oxygen for medical, commercial or industrial purposes, drying of natural gas, drying of air, separation of impurities from a gas stream, separation of some gaseous and liquid product streams and the like. Therefore, it is necessary to agglomerate these zeolite crystals with binder materials to provide an agglomerate mass containing the zeolite crystals, which exhibits a reduced pressure drop.
To overcome these issues and permit the utilization of zeolite crystals, different types of clays have conventionally been used as the binder materials with those crystals, wherein the clay utilized has generally been selected from attapulgite, palygorskite, kaolin, sepiolite, bentonite, montmorillonite, and mixtures thereof. Particularly useful clay binders have been formed using attapulgite clay.
For example, U.S. Pat. No. 2,973,327, discloses the use of a number of different types of clays, including attapulgite, as a binder for molecular sieves.
A particularly useful binder for the production of molecular sieve adsorbent blend products utilize an attapulgite binder comprising highly dispersed attapulgite fibers, as disclosed in U.S. Pat. No. 6,743,745 and U.S. Pat. No. 6,130,179.
Adsorbent materials comprising a type 5A zeolite molecular sieve and a kaolin clay binder, wherein the kaolin comprises from about 10 to about 40% of the composition, are disclosed in U.S. Pat. No. 5,001,098.
Examples of the use of halloysite clays with zeolites for odor remediation and dehumidification are disclosed in U.S. Pat. Nos. 5,667,650 and 5,512,083.
U.S. Pat. No. 6,410,815 discloses the use of halloysite clay as a binder for a zeolite for adsorbing and separating aromatics. However, the binder disclosed in is not present in the final product as it is zeolitized. Other uses of halloysite with zeolites for binderless adsorbents are disclosed in U.S. Pat. Nos. 8,283,274 and 8,859,448.
Halloysite clay is a member of the kaolin clay group. Conventional members of the kaolin clay group include kaolinite, dickite, nacrite, allophane and halloysite. See “Morphology and Structure of Endelite and Halloysite”, The American Mineralogist, July-August 1950, pp 463-484. The chemical formulas for members of the kaolin clay group are similar comprising (OH)8Al4Si4O10, which may be hydrated, resulting in the presence of one or more hydroxyl groups. Chemical formulas for common members of the halloysite clay group include (OH)8Al4Si4O10.4H2O, (OH)8Al4Si4O10.2H2O and (OH)8Al4Si4O10. To distinguish halloysite from the other members of the kaolin group, one reviews the physical structure of the clay particles. The most distinctive difference between members of the halloysite clay group and other members of the kaolin clay group is the physical structure thereof, wherein halloysite clay particles comprise hollow tubes, which may be in the form of cylindrical tubes or nanotubes or split tubes that have collapsed to form laths or ribbons, generally depending on hydration. In contrast, the structure of other members of the kaolin group is generally in the form of hexagonal plates. The structure of the respective members of the kaolin group can be identified using electron microscopy. For a discussion of the structure of halloysite particles and particles of other members of the kaolin group, see, for example, “The American Mineralogist”—Journal of the Mineralogical Society of America, Vol. 35, July-August 1950, Nos. 7 and 8, pp 476-481.
For purposes of this disclosure, “halloysite” includes all forms of the halloysite clay group and may be in the form of hollow tubes or nanotubes or may have collapsed or broken to form laths or ribbons. All such halloysite particles have a similar chemical structure that varies depending on hydration. “Halloysites” included within this disclosure are sometimes referred to as endellite (halloysite) and halloysite (matahalloysite) or simply halloysite.
One problem with many conventionally formed molecular sieve blends is decreased diffusion. It has been recognized that, generally, the larger the diameter of the zeolites, the slower the rate of diffusion of the molecules to be adsorbed. Particularly in the field of pressure swing adsorption, this effect is highly adverse to short cycle time and thus to productivity. Enhanced kinetic values or faster mass transfer rates can result in shorter cycle time and lower power consumption and thus higher adsorbent productivity.
Another important issue in choosing the composition of the molecular sieve blend is its ability to selectively adsorb a compound that is desired to be removed from the processing stream without also adsorbing the component or components of that stream that are not desired to be adsorbed. For example, an important feature of adsorbents used to remove water from an ethanol feed stream is not only their water adsorption capacity but also that the quantity of ethanol that is adsorbed by the adsorbents is limited. Frequently, it is necessary to balance the relative adsorption capabilities of adsorbent blends.
Accordingly, it is one intent to disclose a process for the production of molecular sieve blends using a predominately halloysite binder which blends are effective and highly selective for the production of oxygen for medical, industrial and commercial uses and for removal of water from hydrocarbon feed streams, such as those containing ethanol or cracked gases.
It is a still further intent to disclose molecular sieve blends using as a binder predominately halloysite which blends exhibit enhanced and predictable performance. By reducing the length of bed used (“LUB”), increasing breakthrough time, and increasing tapped bulk density while maintaining the capacity for adsorption and the necessary physical characteristics of the adsorbent, improved adsorbents are disclosed.
It is a still further intent to disclose a process for the production of oxygen for medical, industrial and commercial purposes comprising passing the feedstream over molecular sieve adsorbent blends comprising a zeolite and a halloysite clay binder.
It is a still further intent to disclose molecular sieve blends comprising a zeolite blended with a halloysite clay binder useful for the above described purposes which exhibits enhanced performance.
It is still further intent to disclose a process for production of medical, industrial or commercial oxygen from air, separation of components of a gaseous or liquid feed stream, particularly an ethanol feed stream or an air stream, comprising passing that gaseous or liquid feed stream over molecular sieve blends comprising a zeolite, alternatively a zeolite A or X, and a halloysite clay binder, wherein the binder comprises at least about 90% halloysite clay, alternatively at least about 95% halloysite clay by weight, and in a further alternative 98% halloysite clay.
These and other intents are obtained from the processes for production, the processes for use and the products of the various embodiments disclosed herein.